1. Field of the Invention
The present invention relates to an optical beam scanning apparatus, and more particularly to an optical beam scanning apparatus wherein a rotating polygonal scanner deflects a light beam for scanning.
2. Description of Related Art
In an optical beam scanning apparatus which is to be installed in a printer or in an image reader, conventionally, a polygonal scanner has been provided. The polygonal scanner has a plurality of reflective facets on the periphery. The polygonal scanner is fastened to a rotary shaft of a motor and rotates at a constant speed with the rotation of the motor. Thereby, a light beam is reflected by the reflective facets of the polygonal scanner and deflected at a constant angular velocity.
Such polygonal scanners are generally made of metal like aluminum, or glass. However, in order for lightening, mass production and reduction of cost, U.S. Pat. No. 4,101,365 proposed that polygonal scanners be made of resin.
A polygonal scanner made of metal or glass is so hard that the polygonal scanner is hardly deformed when it is fastened to a rotary shaft of a motor. A polygonal scanner made of resin, on the other hand, is not very hard, and it may be deformed when it is fastened to a rotary shaft of a motor. The deformation of the reflective facets degrades the optical performance of the polygonal scanner.